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    Subject[PATCH 5.4 126/309] ARM: dma-api: fix max_pfn off-by-one error in __dma_supported()
    Date
    From: Chen-Yu Tsai <wens@csie.org>

    commit f3cc4e1d44a813a0685f2e558b78ace3db559722 upstream.

    max_pfn, as set in arch/arm/mm/init.c:

    static void __init find_limits(unsigned long *min,
    unsigned long *max_low,
    unsigned long *max_high)
    {
    *max_low = PFN_DOWN(memblock_get_current_limit());
    *min = PFN_UP(memblock_start_of_DRAM());
    *max_high = PFN_DOWN(memblock_end_of_DRAM());
    }

    with memblock_end_of_DRAM() pointing to the next byte after DRAM. As
    such, max_pfn points to the PFN after the end of DRAM.

    Thus when using max_pfn to check DMA masks, we should subtract one when
    checking DMA ranges against it.

    Commit 8bf1268f48ad ("ARM: dma-api: fix off-by-one error in
    __dma_supported()") fixed the same issue, but missed this spot.

    This issue was found while working on the sun4i-csi v4l2 driver on the
    Allwinner R40 SoC. On Allwinner SoCs, DRAM is offset at 0x40000000, and
    we are starting to use of_dma_configure() with the "dma-ranges" property
    in the device tree to have the DMA API handle the offset.

    In this particular instance, dma-ranges was set to the same range as the
    actual available (2 GiB) DRAM. The following error appeared when the
    driver attempted to allocate a buffer:

    sun4i-csi 1c09000.csi: Coherent DMA mask 0x7fffffff (pfn 0x40000-0xc0000)
    covers a smaller range of system memory than the DMA zone pfn 0x0-0xc0001
    sun4i-csi 1c09000.csi: dma_alloc_coherent of size 307200 failed

    Fixing the off-by-one error makes things work.

    Link: http://lkml.kernel.org/r/20191224030239.5656-1-wens@kernel.org
    Fixes: 11a5aa32562e ("ARM: dma-mapping: check DMA mask against available memory")
    Fixes: 9f28cde0bc64 ("ARM: another fix for the DMA mapping checks")
    Fixes: ab746573c405 ("ARM: dma-mapping: allow larger DMA mask than supported")
    Signed-off-by: Chen-Yu Tsai <wens@csie.org>
    Reviewed-by: Christoph Hellwig <hch@lst.de>
    Cc: Russell King <linux@armlinux.org.uk>
    Cc: Robin Murphy <robin.murphy@arm.com>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/arm/mm/dma-mapping.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- a/arch/arm/mm/dma-mapping.c
    +++ b/arch/arm/mm/dma-mapping.c
    @@ -221,7 +221,7 @@ EXPORT_SYMBOL(arm_coherent_dma_ops);

    static int __dma_supported(struct device *dev, u64 mask, bool warn)
    {
    - unsigned long max_dma_pfn = min(max_pfn, arm_dma_pfn_limit);
    + unsigned long max_dma_pfn = min(max_pfn - 1, arm_dma_pfn_limit);

    /*
    * Translate the device's DMA mask to a PFN limit. This

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